Balls not moving why?

Question

I have made a program to bounce two balls ,but on running the program it is just showing the two balls and they are not moving , I am not able to understand what is the problem? Is there any problem in start of runnable because when I run only single ball it ran whithout implementing Runnable interface but its not working for two why?

      import java.awt.Color;
        import java.awt.Graphics;
        import java.awt.Graphics2D;
        import java.awt.RenderingHints;

        import javax.swing.JFrame;
       import javax.swing.JPanel;



       public class Jpanel extends JPanel implements Runnable{


        Thread t1;
        Thread t2;
        JFrame frame;
        Jpanel jp;
        int x=0;
        int y=0;
        Ball ball=new Ball(this);
        Ball1 ball1=new Ball1(this);
        void move1(){
            ball.move();

        }
        void move2(){
            ball1.move();
        }
        public void paint(Graphics g){


            super.paint(g); 
            setBackground(Color.black);
            Graphics2D g2d=(Graphics2D)g;
             g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON);

            ball.paint(g);
            ball1.paint(g);
        //super.paint(g);//agar yaha to puri screen pehle jaisi saaf ho jaegi           
        }


    public static void main(String args[]) throws InterruptedException{

         Jpanel jp=new Jpanel();
       JFrame frame =new JFrame("Chota Bheem");
       frame.add(jp);
       frame.setBackground(Color.BLACK);
       frame.setSize(500,500);
       frame.setVisible(true);
        frame.setDefaultCloseOperation(frame.EXIT_ON_CLOSE);
       Jpanel t1=new Jpanel();
       Jpanel t2=new Jpanel();
       t1.start();
       t2.start();






         }
       public void start() {
        System.out.println("inside start");
        // TODO Auto-generated method stub
        if(t1==null){
            t1=new Thread(this,"first");
            t1.start();
        }
        if(t2==null){
            t2=new Thread(this,"second");
            t2.start();
        }

    }
     @Override
       public void run() {
        // TODO Auto-generated method stub
            System.out.println("inside run");
        while(true){
            jp.move1();
            jp.repaint();

            try {
                Thread.sleep(1);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

        while(true){
        jp.move2();
        jp.repaint();

        try {
            Thread.sleep(1);
        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        }
    }
    }



      class Ball1{
       Jpanel jps;
      int x=0,y=0,xs=-1,ys=-1;
        public Ball1(Jpanel jpanel) {
        // TODO Auto-generated constructor stub
        this.jps=jpanel;

    }
        public void move(){
       if(x+xs<0){xs=1;}
       else if(y+ys<0){y=-1;}
       else if(x+xs>jps.getWidth()-30){xs=-1;}
       else if(y+ys>jps.getHeight()-30){ys=-1;}

       x=x+xs;
       y=y+ys;

     }
     void paint(Graphics g){
      g.setColor(Color.darkGray);  
      g.fillOval(x, y, 60, 60);
   }
    }




       class Ball{
    int x=0;
    int xs=-1,ys=-1;
    int y=0;
    JPanel jpn;
    Ball(JPanel jpn){
        this.jpn=jpn;
    }

    public void move() {


        if(x+xs<0){
            xs=1;
        }
        else if(y+ys<0){
            ys=1;
        }
        else if(x+xs>jpn.getWidth()-30){
            xs=-1;
        }
        else if(y+ys>jpn.getHeight()-30){
            ys=-1;
        }
        x=x+xs;
        y=y+ys;

    }
    public void paint(Graphics g) {

        jpn.setBackground(Color.black);
        g.setColor(Color.blue);
        g.fillOval(x, y, 50, 50);

    }
}
}

Answer 1

1. This doesn't require multiple threads - I'm not sure why you're adding this complexity
2. If threads were the right thing to use (but they aren't), making your own Jpanel class that is Runnable isn't the right way to do it. What you would want to do is have the Ball class be runnable, and have its position updated in a way that's completely separated from drawing stuff on the screen. Mixing your rendering and movement is not a good separation of concerns. Just have your ball worry about where it is and where it's moving, and let the UI worry about drawing where it is.
3. Swing schedules repaints when it can get around to it, so you're bound to find out at some point that requests to redraw things won't always happen at a consistent frame rate, which may not be what you expect or actually need.
4. If by any chance you're trying to make a game, Swing is going to be a massive waste of your time. What you need is more direct access to screen rendering. Building games with Swing will slowly kill your spirit and make you want to cry. Use something like Slick2D or libgdx instead.
5. The Thread instances you're declaring in your custom Jpanel class aren't even used.
6. Calling Thread.sleep(1) is pretty pointless. Why sleep at all if you're drawing balls on the screen and you're only going to wait about 1 millisecond between ball movements? If you weren't using multiple threads you could either sleep some reasonable amount of time (say, approximately 1/60th of a second) or you could just run at full speed all the time.